In Long-Term Evolution (LTE) Release (Rel) 10, physical downlink channels mainly include: a Physical Downlink Shared Channel (PDSCH), a Physical Broadcast Channel (PBCH), a Physical Multicast Channel (PMCH), a Physical Control Format Indicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH), and a Physical Hybrid Automatic Repeat Request (HARQ) Indicator Channel (PHICH), wherein the PHICH mainly carries ACK/NACK information of an Uplink (UL) HARQ. A plurality of PHICH resources are mapped onto the same Resource Element (RE) to form a PHICH group, wherein PHICHs in the same group are distinguished by different orthogonal sequences. A PHICH resource is represent by a serial number group (nPHICHgroup, nPHICHseq), where nPHICHgroup is a serial number of the PHICH group and nPHICHseq is a serial number of an orthogonal sequence in the PHICH group.
A processing flow of the PHICH is: 1 ACK/NACK bit→repeating for 3 times→Binary Phase-Shift Keying (BPSK) modulation→spectrum spreading→layer mapping and pre-coding→physical resource mapping. The PHICH and the PDCCH are subjected to multiplexing in the same control resource, wherein Table 1 shows durations of the PHICH in a time domain.
TABLE 1Table of durations of PHICH in time domainNon-Multicast-BroadcastSingle-FrequencyMBSFNNetwork (MBSFN) sub-framesub-frameSub-frame 1 andCarrier supportingsub-frame 6 of frameAll otherPDSCH andPHICH durationstructure type 2conditionsPMCHNormal111Extended232
With the development of LTE-Advance carrier aggregation technology, a New Carrier Type (NCT) is proposed in LTE Rel-11, and detailed characteristics of such a carrier are still in discussion. At present, it is confirmed that Cell-specific Reference Signals (CRS) of the singal port of the LTE R8/R9/R10 having a period of 5 milliseconds are applied to perform synchronous tracking in the NCT, demodulation on data and control information in the NCT is based on a Demodulation Reference Symbol (DM-RS), and channel measurement is based on a Channel State Information-Reference Symbol (CSI-RS). Since a traditional Rel-8 PHICH is based on CRS demodulation, and sparse CRSs on the NCT are not used for demodulating data according to the progress of existing Rel-11 protocols, a traditional Rel-8 PHICH structure can be hardly transmitted on the NCT. In the meanwhile, a terminal can only monitor a corresponding PHICH signal on a Component Carrier (CC) to which the terminal sends an UL grant as stipulated by existing R10 protocols, thus an enhanced PHICH (ePHICH) is also required on an NCT used for transmitting an UL grant by using an enhanced PDCCH (ePDCCH). It is necessary to design a new ePHICH structure on the NCT in consideration of demodulation based on a DM-RS and the introduction of the ePDCCH and in order to implement Inter Cell Interference Coordination (ICIC) of a frequency domain.
In a research process of low cost Machine Type Communication (MTC) in Rel-11, since requirements on a transceiving bandwidth of a low cost terminal are lowered and a low cost User Equipment (UE) only need some bandwidths to access. A low cost UE fails to receive PHICHs completely when a system bandwidth is far larger than a transceiving bandwidth of the low cost UE. Besides, there are a large number of low cost UEs, and complicated technologies including Space Division Multiplexing (SDM) and so on are not applied on an UL, it is necessary to consider a new PHICH to ensure transmission of UL data on the low cost UEs at the moment.
In a research of small cells since Rel-12, the number of terminals does not present a great growth compared the number before and only rates of peak data of terminals have been improved, though there are numerous small cells. If HARQ-ACK information of a terminal needs to be transmitted via a macro cell, there may be a collision or a deficiency in capacity according to the original PHICH architecture. Therefore, a new PHICH architecture in the future needs to not only being able to avoid a collision of PHICH resources of different terminals under different small cells via scheduling, but also have a sufficient capacity.
Besides, in a research of cooperation between an authorized spectrum and an unauthorized spectrum, if carrier aggregation is applied, an authorized spectrum is used as a main carrier and an unauthorized spectrum is used as an auxiliary carrier, and the unauthorized spectrum may be scheduled by the main carrier via a certain mechanism. When the main carrier is an LTE system, since a reference signal used in the unauthorized spectrum carrier has not been determined finally, a traditional PHICH structure can be hardly transmitted in the unauthorized spectrum carrier and it is necessary to consider a new PHICH to ensure the reliability of transmission in the unauthorized spectrum carrier.
In conclusion, it is necessary to enhance the design of the PHICH to solve problems including, demodulation performed by using a DM-RS under the NCT, the reliability of UL data transmission of a low cost UE, a conflict of PHICH resource allocation under a small cell, Inter-Cell Interference Coordination (ICIC) of a frequency domain, and the reliability of transmission in an unauthorized spectrum carrier during cooperation of an authorized spectrum and an unauthorized spectrum, and so on.